This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-146517, filed May 26, 1999, the entire contents of which are incorporated herein by reference.
This invention relates to a image pick-up device for taking photographs by use of an electronic image pick-up element and more particularly to a focus detecting device used in the image pick-up device.
Conventionally, various types of image pick-up devices using electronic image pick-up elements are proposed.
For example, in Jpn. Pat. Appln. KOKAI Publication No. 8-262564, there is disclosed a image pick-up device which is a camera of single-lens reflex type for forming an image for observation of a subject by use of a light beam from one photographing lens and has a solid-state image pick-up element instead of a film in the image recording section. In the image pick-up device, a TTL phase difference AF system is used.
Further, in Jpn. Pat. Appln. KOKAI Publication No. 9-274130, a video camera containing a TTL phase difference detecting unit in the photographing lens system is disclosed.
Further, in Jpn. Pat. Appln. KOKAI Publication No. 7-281080, a camera having an electronic view finder is disclosed. In the camera, a light receiving element area for range finding is provided in the image pick-up element for the electronic view finder and a light beam for the electronic view finder is divided and guided to the range finding light receiving element to detect the focus.
However, in the image pick-up device of single-lens reflex camera type disclosed in Jpn. Pat. Appln. KOKAI Publication No. 8-262564 and the video camera disclosed in Jpn. Pat. Appln. KOKAI Publication No. 9-274130, an AF sensor exclusively used for TTL phase difference detection is provided separately from the image pick-up element. Therefore, a problem that the cost is increased occurs.
Further, the camera disclosed in Jpn. Pat. Appln. KOKAI Publication No. 7-281080 is limited to a camera having an electronic view finder.
In addition, there is no concrete disclosure about the range finding light receiving element area, but if it is formed with the same structure as the image pick-up area, the following problem occurs.
Generally, microlenses are disposed on the image pick-up element, the focus detecting light beam of the AF optical system is vignetted by the microlens in the range finding light receiving element area and significant limb darkening occurs thereby causing the range finding precision to be markedly degraded or making it impossible to attain range-finding.
Further, color filters are generally regularly arranged on the front surface of the light receiving element of the image pick-up element and since the arrangement of the color filters is not taken into consideration in the range finding light receiving element area, color information is mixed, thereby making it impossible to attain range-finding.
Since the pitch of pixels of the image pick-up element is determined based on the required image quality of a photographing image, the pitch becomes extremely smaller in comparison with the pixel pitch for the necessary range finding precision in the range finding light receiving element area and it becomes over-specification.
Further, since the pixel area is small, a relatively long storage time is required. In addition, since the number of pixels used for range finding calculation is large, the range finding calculation time is increased and a time lag required for range finding is increased.
Accordingly, an object of this invention is to provide a image pick-up device which is used for taking photographs by use of an electronic image pick-up element and in which it is not necessary to use an exclusive AF sensor which is provided separately from the image pick-up element, the cost thereof can be lowered, the focus detecting precision is enhanced and a time lag due to the focus adjustment can be reduced.
According to a first aspect of this invention, there is provided a image pick-up device comprising a photographing lens; an image pick-up element having an image pick-up area and focus detecting area, for electronically image picking-up a light beam which has passed through the photographing lens; a microlens member disposed only on the front surface of the image pick-up area among the image pick-up area and focus detecting area of the image pick-up element; a focus detecting optical system for re-forming an image on the focus detecting area on the image pick-up element by use of a light beam which is at least part of a light beam of a subject having passed through the photographing lens; an optical member for guiding a light beam which is at least part of the light beam of the subject having passed through the photographing lens towards the focus detecting optical system; and a focus detecting section for detecting the focus based on an output of the image pick-up element.
According to a second aspect of this invention, there is provided a image pick-up device comprising a photographing lens; an image pick-up element having an image pick-up area and focus detecting area, for electronically image picking-up a light beam which has passed through the photographing lens; a color filter member disposed only on the front surface of the image pick-up area among the image pick-up area and focus detecting area of the image pick-up element; a focus detecting optical system for re-forming an image on the focus detecting area on the image pick-up element by use of a light beam which is at least part of a light beam of a subject having passed through the photographing lens; an optical member for guiding a light beam which is at least part of the light beam of the subject having passed through the photographing lens towards the focus detecting optical system; and a focus detecting section for detecting the focus based on an output of the image pick-up element.
According to a third aspect of this invention, there is provided a image pick-up device for dividing a light beam having passed through a photographing lens by use of a main mirror, guiding the divided light beam towards the bottom of a mirror box by use of a sub-mirror, and re-forming an image on an image pick-up element for image pick-up via a phase difference type focus detecting optical system to detect a phase difference, wherein the image pick-up element has an image pick-up area used for electronically image picking-up a light beam having passed through the photographing lens and a focus detecting area used for detecting the focus, and optical elements provided for respective pixels are disposed on the front surface of the image pick-up area.
According to a fourth aspect of this invention, there is provided a camera comprising a photographing lens; an image pick-up element having a first light receiving area used for receiving a light beam having passed through the photographing lens to form an electronic video signal and a second light receiving area used for receiving a light beam having passed through the photographing lens to form a detection signal indicating the focused state of the photographing lens; optical elements provided for respective pixels and arranged not between the photographing lens and the second light receiving area but between the photographing lens and the first light receiving area; and a controller for deriving the focused state of the photographing lens based on the detection signal of the second light receiving area of the image pick-up element.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.